1. Field of the Invention
The present invention relates to improvements in an apparatus for lifting and tilting slats of a slat-ladder in a venetian blind, of a type in which slats are supported by ladder cords, and a motion of either lifting or lowering lift cords, or tapes, enables the slats, first, to be tilted, then, to be lifted or lowered.
2. Description of the Prior Art
Prior art apparatus for lifting and tilting slats of a slat-ladder in a venetian blind, of the type described above, performs the tilting operation in a manner that: the ladder cords are respectively put on, and secured to, each of ladder rings, with the mid portion of the ladder cords positioned on the top of the ladder rings; each of the ladder rings is slippably fitted around each of ladder drums; the ladder drums are arranged to rotate together with a rotating shaft; then, when the shaft is rotated together with the ladder drums, the ladder rings first rotate together with the ladder drums, and thereby the ladder cords are moved together with the ladder drums around the shaft, with the front and the rear sides of the ladder cords shifted to the opposite directions with each other, so that the slats are tilted; when the slats are tilted to a limit, the ladder rings are arranged to engage with a copper and do not rotate any further while starting slippage around the ladder drums, so that the ladder cords are no longer moved around the shaft, and thereby the slats are not tilted any further. Then, the prior art apparatus described above, proceeds to the lifting operation following the end of the tilting operation described above, in a manner that: while the ladder cords stop moving and the tilting motion comes to an end, the lift cords, or tapes, continue to be lifted or lowered so as to lift or lower the ladder, as the shaft continues to be rotated together with lifting drums around which the lift cords are wound for lifting and rewound for lowering. The prior art apparatus described above is disclosed in Japanese Unexamined Utility Model Publication 63127596.
Another prior art mechanism for a venetian blind is disclosed in Japanese Unexamined Utility Model Publication 62118893, for stopping rotation of the rotating shaft when any of the lift cords is slackened. The disclosed mechanism comprises a ratchet wheel disposed on, and constituting a part of, a lifting drum cover which rotates together with the shaft, and a pawl disposed on a holder fixed to a head box so that the pawl may have a rocking motion in the radial direction of the ratchet wheel. The pawl is arranged so that the pawl is normally pressed on, and engaged with, the ratchet wheel, by a spring, and the lift cord is arranged to pass around the pawl. Thereby, when the lift cord is tightened, the pawl is pulled out of the ratchet wheel, and when the lift cord is slackened, the pawl is pressed back by the spring to engage with the ratchet wheel and to stop rotation of the shaft.
Among the components rotatably enclosed in the head box of typical apparatus for tilting and lifting the slats for a venetian blind, the lifting drum cover is largest in its width from the front to the rear, or outdoor, sides.
The shaft rotation stopping mechanism of the prior art apparatus, disclosed above, has a disadvantage in that, since the radially protruding ratchet wheel is disposed around the circumference of the lifting drum cover, and the pawl, radially engaging with the ratchet wheel, is disposed on the holder, the width from the front to the rear sides and the height, of the head box are relatively large in their sizes.
Therefore, smaller head boxes in their width from the front to the rear sides have been desired, since the smaller head boxes in their width from the front to the rear sides, have a better appearance, and are free from any installment space restriction. The present invention is made to satisfy such desire.
In order to obtain a venetian blind having a better appearance, the lift cords, hanging down from the head box, are typically aligned with the ladder cords respectively in line from the front to the rear sides. This alignment has been accomplished in conventional venetian blinds by an arrangement in which the ladder cords, respectively put on, and secured to, each of the ladder rings, hang downward directly from the secured positions on the ladder rings, while the lift cords are pulled around to the positions where the ladder cords hang downward.
The arrangement for the lift cords and the ladder cords, described above, was selected because an alternative, or opposite arrangement has a certain problem. The alternative arrangement is that the lift cords hang downward directly from the lifting drum, while the ladder cords are pulled around to the positions where the lift cords hang downward. The certain problem, described above, with the alternative arrangement, is that the lifting and lowering movements of the slats are significantly heavy, or unsmooth, because the fitting tightness between the ladder rings and the ladder drums of prior apparatus, is arranged to be always constant, while the resistance in the ladder cords becomes greater as they are pulled around, and subsequently, a tighter fitting is required between the ladder ring and the ladder drum for an unchanged lifting smoothness.
The arrangement with the lift cords pulled around, as described above, which is selected in preference to the alternative, as described above, also has a disadvantage in that, in the arrangement where the lift cords are pulled around, the operation of an uneven ladder lowering preventive mechanism, tends to be unreliable, or not very responsive, since the lift cords are arranged to be put on the pawl, which activates the uneven ladder lowering preventive mechanism, or the shaft rotation stopping mechanism, to stop the shaft rotation when the lift cord is slackened.
The prior art apparatus for lifting and tilting slats of a slat-ladder for a venetian blind, described above, has an arrangement in which, the fitting tightness between the ladder rings and the ladder drums is arranged to be constant, as described above, and, in addition, the shaft is required to be further rotated to lift or lower the slat-ladder after the ladder ring is stopped by the stopper, following the slat tilting motion.
Then, the prior art apparatus for lifting and tilting slats, described above, has another disadvantage in that, in case where the fitting tightness between the ladder rings and the ladder drums is set tighter for a better slat tilting responsiveness, the frictional resistance between the ladder rings and the ladder drums becomes greater, whereby the ladder lifting and lowering motion becomes heavier and less smoother; and, in case where the fitting tightness between the ladder rings and the ladder drums is set looser for a lighter slat lifting and lowering motion, slat tilting responsiveness becomes poorer. The present invention is made to solve such problems.